1. Field of the Invention
The invention relates to a method of Physical Vapor Deposition (PVD) as related to submicron integrated circuits on semiconductor wafers, and more particularly to the physical vapor deposition of refractory metals in submicron vias and lines.
2. Description of the Related Art
Copper is one of the promising conductors for next generation ultra large scale integration (ULSI) metallization because of its low resistivity and high resistance to electromigration. However, successful implementation of copper metallization requires a proper choice of adhesion layer/diffusion barrier materials and deposition techniques, passivation layer, and a suitable means of filling vias and trenches with copper. Good bottom coverage has been achieved using ionized PVD techniques. The major drawback of this technique is poor sidewall coverage due to directional ion flux, which is the major concern for a copper barrier layer deposition.
U.S. Pat. No. 5,403,779 (Joshi et al.) shows a method of depositing metal lines using PVD techniques. Conductive lines and vias are created using a combination of both PVD (e.g., evaporation or collimated sputtering) of a low resistivity metal or alloy followed by Chemical Vapor Deposition (CVD) of a refractory metal and subsequent planarization. Collimated sputtering allows for creating a refractory metal liner in an opening in a dielectric which is suitable as a diffusion barrier to copper based metallizations as well as CVD tungsten. Ideally, for faster diffusing metals like copper, liners are created by a two step collimated sputtering process wherein a first layer is deposited under relatively low vacuum pressure where directional deposition dominates (e.g., below 1 mTorr) and a second layer is deposited under relatively high vacuum pressure where scattering deposition dominates (e.g., above 1 mTorr).
U.S. Pat. No. 5,250,465 (Iizuka et al.) discloses producing a semiconductor device having small diameter via holes, particularly not greater than 0.6 microns, for a multilayer interconnection, by a method comprising covering an interlayer film and via holes with a continuous first metal film by a CVD process, and heating and melting by an irradiation of an energy beam a second metal film deposited on the first film by a PVD process, together with the first metal film, to fully fill the via holes with the material from the outside of the holes, to thus form conductive plugs therein.
C. Y. Chang, S. M. Sze, in ULSI Technology, by The McGraw-Hill Company, Inc. copyright 1997, pp. 378-387 discusses physical vapor deposition techniques.